The goal of the proposed research is to develop a more reliable method for assessing individual differences in how newborn infants respond to visual and auditory stimuli. Prior research suggests that neonates' capacity to orient and respond to what they see and hear, especially the caretaker's face and voice, may influence early mother-infant interaction; however, the observer rating scales commonly used to assess responsiveness and orientation behavior have demonstrated reliability concerns and often show no relation to later behavior. There is increasing evidence that heart rate measures may reliably assess individual differences in infant attention and responsiveness. Additional research is now needed to explore the link between newborn cardiac response to environmental stimuli and subsequent social interaction. The proposed research does so with a short-term longitudinal design. In the neonatal period we will monitor heart rate as 2-week-old infants are presented with animate and inanimate visual and auditory stimuli. Cardiac response (change in heart rate) to these stimuli, as well as baseline heart rate variability and behavioral orientation ratings, will be related to social interaction measures of both mother and infant obtained at 4 months of age. Subjects will be 70 mother infant pairs from an economically-disadvantaged, rural Appalachian population at risk for less optimal mother-infant interaction. Since the quality of early mother-infant interaction has repeatedly been associated with children's social and cognitive development, knowledge concerning the infant's contribution to interaction gained from this study may have application to early intervention programs.